In a numerical control (NC) machine tool, it has been a general practice that a plurality of operators such as an operator who inputs a control program of an NC apparatus and causes the NC apparatus to execute work and an operator who monitors a state during the work and checks that the NC apparatus is normally operating operate the NC machine tool and monitor a state of the NC machine tool. In this case, it is necessary to prevent wrong operation by an inexperienced operator or a leak of information such as a control program or a control parameter by a malicious operator. Technologies for preventing the wrong operation and the leak have been proposed.
For example, there has been proposed an apparatus that, when the NC machine tool is broken, checks, using an RFID (Radio Frequency Identification), whether an operator is an operator having a recovery operation ability and prevents recovery work from a failure by an inexperienced operator (see, for example, Patent Literature 1). There has been proposed a plant control system in which a user carries a transmission device that transmits a user ID and the system limits an operation range on the basis of the user ID read by a user-ID reading device and records an operation history of each user (see, for example, Patent Literature 2).